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-   -   A couple of noob concrete finishing questions (http://www.diychatroom.com/f19/couple-noob-concrete-finishing-questions-112164/)

SMRcalidiv 07-27-2011 01:57 PM

A couple of noob concrete finishing questions
 
Hey Guys, love this site...I have been lurking here for awhile and learned lots of info, thanks!

I have two concrete finishing questions, FRAT warning, but first here's the background story.

I recently decided to extend the walkway on the side of my home and my first attempt turned out like hammered crap. I am using pre-mixed Sakrete from HD. I followed the water/mix ratio on the bag and the concrete was too dry, I also didn't float immediately as I misunderstood the waiting for the bleed water to disappear step. I screeded, then waited, then tried to float...FAIL. So, being the stubborn and anal kind of guy that I am I refused to be beaten and gave it another go by making a 48" x 12" paver/slab (I think it looks modern and unique, anyway..that's beside the point). On my second attempt I added another 1/2 qt of water..perfect wetness, SCORE...then I poured, screeded, floated, edged, let bleed water disappear...and finish troweled, then brush finished. WAY BETTER results, but far from perfect...as I still have little pit areas where the finish is not fully smooth/brushed...and you can see a little aggregate. SO...on to my questions.

1. I saw on a DIY show where they mixed a little extra slurry to go back and fill in these rough spots/pits...What would you suggest to fix these spots?

2. I saw a "Pro Finish Quickrete" at Lowe's. It was a little more expensive per bag but if it finishes easier/better I can see switching brands. Have you guys used this and is there a noticeable difference?

Thank you for taking the time to read this, and in advance for any help or guidance. I realize that concrete finishing is not something that can be learned in a day/week/month or even a year...so I appreciate any tips you can give that have probably come from years of experience.

Justin

mustangmike3789 07-27-2011 06:42 PM

I have never used that product . When in a pinch we have used"hot patch" (can't recall the brand name) concrete topping sold at HD to fill void and low spots and it holds up good.

SMRcalidiv 07-28-2011 01:22 PM

Thanks for the response, I saw a video, on the concretenetwork I believe, where they were fixing small cracks in newly poured and stamped slabs by using a cement only slurry to fill them. What do you think of this? For reference the pits I am talking about are only the size of lets say a piece of aggregate that came dislodged, not necessarily a low spot that would be large enough to puddle or anything.

jomama45 07-28-2011 07:11 PM

I believe what you are referring to, the small holes, are what we call "cat eyes". They occur when small torpedo stone are close to the surface and get displaced during the finishing process. What happens is the trowel catches these stones and tips them over. Generally from a number of things including too much pressure and/or angle on the trowel, the stones being too close to the surface, and most likely in your case, excessive bleed water which results in low cement content at the surface.

I actually dealt with a few "Cat eyes" today on a garage slab with a finishing machine. We poured over a vapor barrier and the weather is very humid, and the result was a little bit of bleed water present at the surface. Not much yo can do with it once it starts, other than trowel lightly or, in my case, wait for the concrete to get a tad harder to finish.

For small pours where you want to mix your own concrete, I would highly recommend using at least 30-40% of the fast setting/red bag Quikcrete. It bleeds far less than the other Quikcrete, making the the stone rolling far less common. And don't be afraid to work the surface with a wood hand float a bit when the surface is whet, as this can certainly help bring more "cream" to the surface, which will be far easier to finish than the small aggregate.

SMRcalidiv 07-28-2011 09:42 PM

Thanks for your responses, here is the best way I can describe my finishing problem...I don't think that there was enough bleed water or that the mix was too dry to allow the larger stones to be forced down when I floated it with a wooden float when it was wet. This left areas where the stones were able to be pushed down and the cream could rise and areas where the aggregate just wasn't budging...thus leaving a few pit marks where the workable cream wouldn't spread or cover all of the exposed aggregate. I have started to consider a few things that I would appreciate insight into:

1. Accepting that the Sakrete brand of concrete just has a higher aggregate ratio than delivered mixes. I did go and buy a bag of the Pro Finish Quikrete to try for comparison.

2. I need to add a touch more water than the 3qts recommended on the bag per 60lbs. I have been watching every video or tv show that I can find in which they are having concrete work done and every pour I see looks significantly more wet than mine. I do realize that overwatering the mix will weaken the concrete so I don't want to sound irresponsible with the water, but when I try to float it, immediately after screeding, I simply cannot push the larger aggregate down.

3. This one is a given...I JUST NEED MORE PRACTICE:)

jomama45 07-29-2011 09:49 AM

If you use the red bag Quikcrete, along with the regular 4000 psi you'll have adequate strength for any sidewalk even with a tad more water. The biggest problem I've encountered with the non-ready-mix concrete, such as Quikcrete, is that it's not air-entrained, and usually the top delaminates from freeze-thaw cycles in our climate. The red bag helps hold the bleed water to a minimum, and that helps the concrete resist the delaminating problems.

SMRcalidiv 07-29-2011 12:41 PM

Ok, thanks...luckily I live in CA so I am not really concerned with freezing temps as we might see one day below 32 a year...maybe.

I am going to try the Quikrete 5000 Pro Finish today, as I already have the bag sitting here taunting me. After that I will go and pick up a red bag to try as well. Luckily these pavers allow me to test different brands an mixes as they will be separate from each other and I'm going to stain them so they will all look similar in the end.

What do you guys recommend for someone trying to learn, a mix that is on the dry side or a touch on the wet (not soupy) side?

jomama45 07-29-2011 05:38 PM

A "little" bit wetter will be easier to work with than a drier/stiffer mix.

SMRcalidiv 07-30-2011 12:38 AM

1 Attachment(s)
Thanks Jomama, I went to Lowe's today and picked up a 50lbs. red bag and an 80lbs. regular bag to mix together to get a 40% ratio of fast setting and I'll try that mix tomorrow.

I did manage to pour a slab using the Pro Finish Quikrete and I would say that it did finish a lot better than the previous regular Sakrete did. Either it was actually an easier product to work with or I just got a little better, but I still had the rough patches and there wasn't enough slurry or bleed water to work with at the time of finish troweling to spread, even after tamping it a little with the trowel to try to produce some..so I think I could make the next batch a little bit wetter.

I also had an epiphany, or just a massive brain fart, could the lack of smoothness be attributed to the fact that I am using a wood float in the initial floating as opposed to a mag float?

Here is a pic so you can see what I am talking about...be gentle...I'm a rookie

SMRcalidiv 07-30-2011 04:22 PM

Red bag mix= EPIC FAIL...ugh...it set up way too fast and was just a complete disaster. I think that the fast setting nature of the product mixed with the hot CA sun was a recipe for failure...oh well...gotta keep trying before I lose all motivation to continue this project. Wish me luck lol

jomama45 07-31-2011 11:34 AM

Quote:

Originally Posted by SMRcalidiv (Post 696934)
Red bag mix= EPIC FAIL...ugh...it set up way too fast and was just a complete disaster. I think that the fast setting nature of the product mixed with the hot CA sun was a recipe for failure...oh well...gotta keep trying before I lose all motivation to continue this project. Wish me luck lol

Sorry to hear that, I think I underestimated the low humidity you may have there. Here, the problem is excessive bleed water at the surface, creating very long surface-set times & poor finish quality.

You're fine in using the wood float in the begining but you should probably switch to magnesium after the initial floating.

SMRcalidiv 07-31-2011 07:27 PM

Ok, so I broke up the fubar'd slab I poured yesterday, and re-poured it and another one using regular old Quikrete, not the pro finish 5000. I also picked up an aluminum float to do this with. I made the mix a tad wetter this time and the whole combination turned out pretty decently. I am pretty happy with the progress but I still think it could be better. There are times where it looks very smooth, but then as the bleed water soaks in or dries I get little pits or cateyes, but nothing too horrible.

On a side note, I took the extra mixed concrete that was in the wheelbarrow and put it in a little form I made on a board. The little 10"x8" slab turned out amazingly smooth with pretty much nothing done to it. Is this a result of the solid board underneath not allowing the slurry or bleed water to drain out of the bottom? I am starting to think that the rocks I am using as my base may be too large and allowing too much drainage.


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